This invention relates to a breathable laminate (i.e., breathable to water vapor but substantially liquid-impermeable) which is permanently conformable to the contour of a wearer. The laminate stretches as needed to conform to the contour of the wearer and remains, essentially, in its extended or stretched state, even after a stretching force is removed.
Laminates which are breathable to water vapor but substantially impermeable to liquid water are known in the art, and are commonly used in diaper backings, other personal care absorbent garments, medical garments and the like. These laminates may be composed of a breathable, stretch-thinned filled film and a spunbond web. The breathable film can be formed by blending one or more polyolefins with an inorganic particulate filler, forming a film from the mixture, and stretching the film to cause void formation around the filler particles. The resulting film may have thin polymer membranes around the filler particles which permit molecular diffusion of water vapor, while the overall film substantially blocks transmission of liquid water, or may have micropores going through the film. The breathable film can be laminated to a nonwoven web, for instance, a spunbond web, by thermal or adhesive bonding. The spunbond web adds strength and integrity to the breathable laminate, and provides a soft, cloth-like feel.
One trend affecting the personal care absorbent garment industry, and the medical garment industry, involves the demand and need for products with higher breathability to water vapor, which retain or increase the barrier to water, blood and other liquid substances. This trend reflects the demand for increased wearer comfort without loss of barrier performance. Another trend affecting these industries involves the demand and need for products having better fit, which conform to the contours of the wearer""s body. To date, much of the investigation in this area has involved use of elastic materials.
One challenge involving the use of elastic materials is that many of the products, including absorbent garments, have a complex layer structure. Absorbent garments typically include at least a liquid-permeable top layer, an absorbent core layer, and a breathable, substantially liquid-impermeable outer cover laminate. If one of these materials is made elastic, the absorbent garment will not necessarily be elastic. In order for the absorbent garment to have elastic properties, each layer must either a) exhibit a desired minimum level of stretching and retraction or b) be xe2x80x9cfree floatingxe2x80x9d and not attached to the elastic or extendible layers.
Another challenge of using elastic materials to promote conformability is the conversion of kinetic energy to potential energy during stretching. The stored potential energy in the stretched regions of the garment creates a retractive force which acts against the wearer""s body, causing compression of the skin and discomfort.
Wherever an elastic garment is stretched in selected regions to conform to a wearer""s body, the garment will exhibit a tighter fit in the stretched regions. Skin ripples, red marks or even rashes may form where the elastic material exhibits the greatest retractive force against the wearer""s skin. These problems become more acute when the garment contains more than one elastic layer.
There is a need or desire in the industries of personal care absorbent garments and medical garments, for less expensive materials which stretch in order to conform to the contours of a wearer""s body. There is also a need or desire for materials which do not store significant amounts of potential energy when stretched, and which do not exhibit excessive retractive force against the wearer""s body. In short, there is a need or desire for materials and garments which remain stretched, i.e., which permanently conform to the contours of the wearer""s body.
The present invention is directed to a substantially liquid-impermeable laminate including at least one thermoplastic nonwoven filament web and at least one film, preferably a breathable, substantially liquid-impermeable film laminated to it. The laminate (which is preferably breathable) has a machine direction (direction of formation) which corresponds to a primary direction of orientation of the nonwoven filaments, and a cross direction which is perpendicular to the machine direction. The breathable laminate is extendible in the cross direction to a stretched width that is at least 25% greater than an original, unstretched width upon application of a stretching force. When the stretching force is removed, the breathable laminate either does not retract, or retracts by not more than 30% of the difference between the stretched width and the original width.
The breathable, substantially liquid impermeable laminate preferably includes a breathable, microporous film having cross-directional extendibility at least as great as the laminate, and a fibrous nonwoven web, bonded to the film, which also has cross-directional extendibility at least as great as the laminate. The film may alternatively be made of an inherently breathable polymer. The component which has the least cross-directional extendibility (whether the film or the web) will limit the useful cross-directional extendibility of the entire laminate. In other words, the laminate will extend to the same or a lesser extent than the least extendible layer. Similarly, neither the film nor the web should exhibit significantly more retractive force than is desired for the laminate in general. If either the film or the web has a tendency to retract by more than 30% of the difference between its stretched width and original unstretched width, then the overall laminate may retract too much or apply excessive retractive force against the wearer""s body.
In one embodiment, the thermoplastic nonwoven filament web is a neck-stretched nonwoven web, for example, a neck-stretched spunbond web. The nonwoven web, which is made of a relatively inelastic polymer material, is extended in the machine direction to cause narrowing or neck-in of the web in the cross direction. The web is laminated and bonded to a breathable microporous film while the web is in the necked condition. The film includes at least one thermoplastic polymer which renders the film stretchable (but not elastic, or highly retractable) in the cross direction. Thus, when the laminate is stretched in the cross direction, the film is stretched, and the nonwoven web returns toward its original, un-necked state. The stretched laminate exhibits little or no retractive force after being held for one minute in the stretched condition. In this embodiment, the laminate has cross-directional extendibility but may not have machine direction extendibility if the nonwoven web is made from a non-extendible polymer composition.
In another embodiment, the thermoplastic nonwoven web is not necessarily neck-stretched, but is made using an extendible (but not elastic, or highly retractable) polymer material. The film also includes at least one thermoplastic polymer which renders the film extendible (but not elastic, or highly retractable) in the cross direction. When the laminate is stretched in the cross direction, the film is stretched, and the fibers in the nonwoven web are also stretched. The stretched laminate exhibits little or no retractive force. In this embodiment, the laminate may have extendibility in the machine direction as well as the cross direction, since both the film and web are made from extendible polymers.
In another embodiment, the thermoplastic web is not necessarily neck-stretched or made using a stretchable polymer. Instead, the nonwoven web is rendered stretchable by crimping of the filaments. Crimped filaments have undulations and/or spirals along their length which tend to straighten out when a stretching force is applied, thus rendering the filaments elongatable. Again, the film includes at least one thermoplastic polymer which renders the film stretchable (but not elastic, or highly retractable) in the cross direction. When the laminate is stretched in the cross direction, the film is stretched, and the crimped filaments of the nonwoven web tend to straighten out. Again, the stretched laminate exhibits little or no retractive force. In this embodiment, the laminate may have extendibility in the machine direction as well as the cross direction, since the film is made from an extendible polymer and the web will extend in either direction.
With the foregoing in mind, it is a feature and advantage of the invention to provide a substantially liquid-impermeable (preferably breathable) laminate which stretches where needed, and exhibits little retractive force, thereby conforming permanently to the contour of a wearer""s body.
It is also a feature and advantage of the invention to provide a laminate which conforms to the contours of a wearer""s body, and which is relatively inexpensive to manufacture compared to prior art elastic laminates.
It is also a feature and advantage of the invention to provide various personal care and medical garments which incorporate the breathable laminate of the invention, and which (due to their extendibility and low retractions) permanently conform to the contour of a wearer""s body.
The foregoing and other features and advantages will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are intended to be illustrative rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof
The term xe2x80x9cextendiblexe2x80x9d is used herein to mean a material which upon application of a stretching force, can be extended in a particular direction, to a stretched dimension (e.g., width) which is at least 25% greater than an original, unstretched dimension. When the stretching force is removed after a one-minute holding period, the material does not retract, or retracts by not more than 30% of the difference between the stretched dimension and the original dimension. Thus, a material having a width of one meter, which is extendible in the cross direction, can be stretched to a width of at least 1.25 meters. When the stretching force is released, after holding the extended width for one minute, a material stretched to a width of 1.25 meters will not retract, or will retract to a width of not less than 1.175 meters. Extendible materials are different from elastic materials, the latter tending to retract most of the way to their original dimension when a stretching force is released. The stretching force can be any force sufficient to extend the material to between 125% of its original dimension, and its maximum stretched dimension in the selected direction (e.g., the cross direction) without rupturing it.
The xe2x80x9cpercent retractionxe2x80x9d is determined when the retractive force drops below 10 grams for a 3-inch wide sample, using the procedure set forth in the Examples. xe2x80x9cPercent permanent setxe2x80x9d is 100 minus xe2x80x9cpercent retraction.xe2x80x9d The term xe2x80x9cinelasticxe2x80x9d refers both to materials that do not stretch by 25% or more and to materials that stretch by that amount but do not retract by more than 30%. Inelastic materials include extendible materials, as defined above, as well as materials that do not extend, e.g., which tear when subjected to a stretching force.
The term xe2x80x9cmachine directionxe2x80x9d as applied to a nonwoven web, refers to the direction of travel of a conveyor passing beneath the spinnerette or similar extrusion or forming apparatus for the filaments, which causes the filaments to have primary orientation in the same direction. While the filaments may appear wavy, or even randomly oriented in a localized section of a nonwoven web, they usually have an overall machine direction of orientation which was parallel to the movement of the conveyor that carried them away from the extrusion or forming apparatus.
The term xe2x80x9cmachine directionxe2x80x9d as applied to a film, refers to the direction on the film that was parallel to the direction of travel of the film as it left the extrusion or forming apparatus. If the film passed between nip rollers or chill rollers, for instance, the machine direction is the direction on the film that was parallel to the surface movement of the rollers when in contact with the film.
The term xe2x80x9cmachine directionxe2x80x9d as applied to a laminate including at least one film and at least one nonwoven web, refers to the machine direction of the nonwoven web component of the laminate.
The term xe2x80x9ccross directionxe2x80x9d for a nonwoven web, film, or laminate refers to the direction perpendicular to the machine direction. Dimensions measured in the cross direction are referred to as xe2x80x9cwidthxe2x80x9d dimensions, while dimensions measured in the machine direction are referred to as xe2x80x9clengthxe2x80x9d dimensions.
The terms xe2x80x9cbreathable film,xe2x80x9d xe2x80x9cbreathable laminatexe2x80x9d or xe2x80x9cbreathable outer cover materialxe2x80x9d refer to a film, laminate, or outer cover material having a water vapor transmission rate (xe2x80x9cWVTRxe2x80x9d) of at least about 300 grams/m2xe2x80x9424 hours, using the WVTR Test Procedure described herein. The term xe2x80x9chigher breathabilityxe2x80x9d simply means that a second material has a higher WVTR than a first material. Breathable materials typically rely on molecular diffusion of vapor, or vapor passage through micropores, and are substantially liquid impermeable.
The term xe2x80x9cliquid water-permeable materialxe2x80x9d refers to a material present in one or more layers, such as a nonwoven fabric, which is porous, and which is liquid water permeable due to the flow of water and other aqueous liquids through the pores. The spaces between fibers or filaments in a nonwoven web can be large enough and frequent enough to permit leakage and flow of liquid water through the material.
The term xe2x80x9cnonwoven fabric or webxe2x80x9d means a web having a structure of individual fibers or threads which are interlaid, but not in a regular or identifiable manner as in a knitted fabric. Nonwoven fabrics or webs have been formed from many processes such as, for example, meltblowing processes, spunbonding processes, air laying processes, coforming processes, and bonded carded web processes. The basis weight of nonwoven fabrics is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fiber diameters useful are usually expressed in microns. (Note that to convert from osy to gsm, multiply osy by 33.91.)
The term xe2x80x9cmicrofibersxe2x80x9d means small diameter fibers typically having an average fiber denier of about 0.005-10. Fiber denier is defined as grams per 9000 meters of a fiber. For a fiber having circular cross-section, denier may be calculated as fiber diameter in microns squared, multiplied by the density in grams/cc, multiplied by 0.00707. For fibers made of the same polymer, a lower denier indicates a finer fiber and a higher denier indicates a thicker or heavier fiber. For example, the diameter of a polypropylene fiber given as 15 microns may be converted to denier by squaring, multiplying the result by 0.89 g/cc and multiplying by 0.00707. Thus, a 15 micron polypropylene fiber has a denier of about 1.42 calculated as (152xc3x970.89xc3x970.00707=1.415). Outside the United States the unit of measurement is more commonly the xe2x80x9ctex,xe2x80x9d which is defined as the grams per kilometer of fiber. Tex may be calculated as denier/9.
The term xe2x80x9cspunbonded fibersxe2x80x9d refers to small diameter fibers which are formed by extruding molten thermoplastic material as filaments from a plurality of fine capillaries of a spinnerette having a circular or other configuration, with the diameter of the extruded filaments then being rapidly reduced as by, for example, in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartmann, U.S. Pat. No. 3,502,538 to Petersen, and U.S. Pat. No. 3,542,615 to Dobo et al., each of which is incorporated herein in its entirety by reference. Spunbond fibers are quenched and generally not tacky when they are deposited onto a collecting surface. Spunbond fibers are generally continuous and often have average deniers larger than about 0.3, more particularly, between about 0.6 and 10.
The term xe2x80x9cmeltblown fibersxe2x80x9d means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity heated gas (e.g., air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed for example, in U.S. Pat. No. 3,849,241 to Butin et al. Meltblown fibers are microfibers which may be continuous or discontinuous, are generally smaller than about 1.0 denier, and are generally self bonding when deposited onto a collecting surface.
The term xe2x80x9cfilmxe2x80x9d refers to a thermoplastic film made using a film extrusion process, such as a cast film or blown film extrusion process. This term includes films rendered microporous by mixing polymer with filler, forming a film from the mixture, and stretching the film.
The term xe2x80x9cmicroporousxe2x80x9d refers to films having voids separated by thin polymer membranes and films having micropores passing through the films. The voids or micropores can be formed when a mixture of polymer and filler is extruded into a film and the film is stretched, preferably uniaxially in the machine direction. Microporous films tend to have water vapor transmission due to molecular diffusion of water vapor through the membranes or micropores, but substantially block the passage of aqueous liquids.
The term xe2x80x9cpolymerxe2x80x9d includes, but is not limited to, homopolymers, copolymers, such as for example, block, graft, random and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term xe2x80x9cpolymerxe2x80x9d shall include all possible geometrical configurations of the material. These configurations include, but are not limited to isotactic, syndiotactic and atactic symmetries.
The term xe2x80x9cabsorbent articlexe2x80x9d includes personal care absorbent products and medical absorbent products. The term xe2x80x9cpersonal care absorbent productxe2x80x9d includes without limitation diapers, training pants, swim wear, absorbent underpants, baby wipes, adult incontinence products, and feminine hygiene products.
The term xe2x80x9cmedical absorbent productxe2x80x9d includes without limitation absorbent garments, underpads, bandages, face masks, absorbent drapes, and medical wipes.
The term xe2x80x9cneckxe2x80x9d or xe2x80x9cneck stretchxe2x80x9d interchangeably means that the fabric, nonwoven web or laminate is drawn such that it is extended under conditions reducing its width or its transverse dimension by stretching lengthwise or increasing the length of the fabric. The controlled drawing may take place under cool temperatures, room temperature or greater temperatures and is limited to an increase in overall dimension in the direction being drawn up to the elongation required to break the fabric, nonwoven web or laminate, which in most cases is about 1.2 to 1.6 times. When relaxed, the fabric, nonwoven web or laminate does not return totally to its original dimensions. The necking process typically involves unwinding a sheet from a supply roll and passing it through a brake nip roll assembly driven at a given linear speed. A take-up roll or nip, operating at a linear speed higher than the brake nip roll, draws the fabric and generates the tension needed to elongate and neck the fabric. U.S. Pat. No. 4,965,122 issued to Morman, and commonly assigned to the assignee of the present invention, discloses a reversibly necked nonwoven material which may be formed by necking the material, then heating the necked material, followed by cooling and is incorporated herein by reference in its entirety. The heating of the necked material causes additional crystallization of the polymer giving it a partial heat set. If the necked material is a spunbond web, some of the fibers in the web may become crimped during the necking process, as explained in U.S. Pat. No. 4,965,122.
The term xe2x80x9cneckable materialxe2x80x9d or xe2x80x9cneckable layerxe2x80x9d means any material or layer which can be necked such as a nonwoven, woven, or knitted material, or a laminate containing one of them. As used herein, the term xe2x80x9cnecked materialxe2x80x9d refers to any material which has been drawn in at least one dimension, (e.g., lengthwise), reducing the transverse dimension, (e.g., width), such that when the drawing force is removed, the material can be pulled back to its original width. The necked material generally has a higher basis weight per unit area than the un-necked material. When the necked material is pulled back to its original width, it should have about the same basis weight as the un-necked material. This differs from stretching/orienting the film layer, during which the film is thinned and the basis weight is reduced. Preferred nonwoven webs for use in the invention are made from an inelastic polymer.
The term xe2x80x9cpercent neckdownxe2x80x9d refers to the ratio determined by measuring the difference between the un-necked dimension and the necked dimension of the neckable material and then dividing that difference by the un-necked dimension of the neckable material.